Oil based formulations for active personal care and pharmaceutical products have certain desirable properties in that they are non-drying, skin friendly compositions which can be derived from materials that are readily available and inexpensive to produce. However, while current carriers, described in U.S. Pat. Nos. 5,015,708; 6,177,068; 6,255,421; 6,255,422 and 6,300,442, are produced by polymerization of monomers in an oil base, the monomeric materials employed are not inherently water insoluble, hence their polymeric products are prone to leaching under extended exposure to high humidity or water environments. This shortcoming is particularly undesirable in carriers employed for suntan or UV blocking formulations. Further, such leachable carriers may be harmful for topically applied pharmaceuticals since the concentration of the active material in the formulation may become harmfully elevated.
Accordingly, it is an object of this invention to provide a water leach-resistant carrier which is compatible with a wide variety of active chemicals and which is inexpensive and easily produced.
Other advantages of the present invention will become apparent from the following description and disclosure.
In accordance with this invention there is provided a leach resistant carrier composition for active cosmetic and pharmaceutical formulations which comprises, an exclusively water insoluble polymer or polymer mixture including a water insoluble acrylate and/or a water insoluble acrylamide polymer dissolved in oil and derived from the anhydrous, free radical initiated solution polymerization of a corresponding water insoluble monomer or monomers in an oil base or solvent. For the purpose of this invention, the term xe2x80x9cacrylatexe2x80x9d is intended to include both acrylates and methacrylates and is referred to herein as (meth)acrylate. Similarly, xe2x80x9cacrylamidexe2x80x9d is intended to include acrylamides and methacrylamides and is indicated herein as (meth)acrylamide.
In the preparation of the present polymer carrier compositions, it is essential that the oil during monomer polymerization and in the polymerized product be maintained at between 40 and 90 wt. %, preferably at least equal portions of polymer and oil and most preferably an excess of oil in the range of from 60 to 70 wt. %. At oil concentrations below 40 wt. %, the product is too viscous for easy formulation with active or other components. It is equally important to monitor the initiator feed continuously or in increments throughout the reaction so as to maintain a concentration of from about 0.1 to about 10 wt. %, preferably from 0.2 to 5 wt. % with respect to monomer present in the reactor.
In general, the polymerization is effected under a blanket of nitrogen at a temperature of between about 50xc2x0 and about 150xc2x0 C. with agitation over a period of from about 2 to about 25 hours.
The monomeric components, from which the present polymers are derived, are exclusively water insoluble monomers selected from the group consisting essentially of a C8 to C30 alkyl substituted (meth)acrylate; a Nxe2x80x94C8 to C30 alkyl (meth)acrylamide; a C1 to C6 alkyl (meth)acrylate; a Nxe2x80x94C1 to C6 alkyl (meth)acrylamide and mixtures thereof. The monomeric mixture may optionally include up to 50 wt. %, preferably not more than 25 wt. %, of another water insoluble monomer such as, styrene, vinyl chloride, 2-vinyl pyridine, 4-vinyl pyridine, an ethylenically unsaturated ester, for example a C6 to C18 alkyl-cinnamate, -maleate or -crotonate and the like; as well as up to 10 wt. % of a water soluble polymerizable monomer such as, for example, vinyl amide, vinylpyrrolidone, vinyl caprolactam, hydroxyalkyl (meth)acrylate, (meth)acrylic acid, cinnamic acid, N,N-dimethylamoniethyl methacrylate, N,N-dimethylaminopropyl (meth)acrylamide and mixtures of the foregoing monomers. Such optional monomers can be added to neutralize the monomeric component to a pH of about 7 in a subsequent formulation which will assure stability of an o/w emulsion.
The monomer component may also include up to 5 wt. % of a crosslinking agent. Suitable crosslinking agents include, but are not limited to, diallylimidolidone, the divinyl ether of diethylene glycol, pentaerythritol triallyl ether (PETA), triallyl-1,3,5-triazin-2,4,6-(1H, 3H, 5H)trione (TATT), ethylene glycol diacrylate, 2,4,6-triallyloxy-1,3,5-triazine, N-vinyl-3-(E)-ethylidenepyrrolidone (EVP), 1,7-octadiene, 1,9-decadiene, divinyl benzene, methylene-bis(methacrylamide) methylene-bis(acrylamide), N,N-divinylimidazolidone, ethylidene-bis(N-vinylpyrrolidone) (EBVP) and bis(N,N-acrylamide) and mixtures thereof.
The above optional monomers can be added to neutralize the monomeric mixture to pH of about 7 in the formulation which may improve the stability of an o/w emulsion.
The preferred monomer is a mixture of long and short chain (meth)acrylates and/or (meth)acrylamides, particularly mixtures of acrylates and methacrylates.
The oil base of the present composition contains a cosmetically or pharmaceutically acceptable, non-volatile, water repellant material having a viscosity of from about 5 to about 600,000 centistokes, preferably from about 10 to about 300 centistokes, at 25xc2x0 C. Representative examples of suitable bases include individual oils or mixtures which include light and heavy mineral oils, silicone oils, plant and animal oils and water insoluble esters such as esters, e.g. the isocetyloleate, stearyl laurate, isopropyl adipate, isopropyl myristate or isocetyl stearate and mixtures thereof. The oil base may contain up to 15 wt. %, more often from 5 to 10 wt. %, of a glycol such as propylene glycol, pentanediol, methyl-pentanediol and mixtures of such.
Suitable siloxane oils are selected from non-volatile silicones, such as polyalkyl siloxanes, polyaryl siloxanes, polyalkylaryl siloxanes and polyether siloxane copolymers; and volatile silicones such as cyclomethicones also may be used.
Non-volatile polyalkylsiloxanes thus include, for example, polydimethylsiloxanes (Dimethicone) with viscosities ranging from about 5 to about 600,000 centistokes (cS) at 25xc2x0 C. These siloxanes are available, for example, from the General Electric Company as the VISCASIL series and from Dow Corning as the Dow Corning 200 products. Their viscosity can be measured by the glass capillary viscometer procedure set forth in Dow Corning Corporate Test Method CTM 0004 issued Jul. 20, 1970. Preferably, the viscosity of these siloxanes selected have a viscosity of about 100 to about 100,000 cS, and most preferably, a viscosity of up to about 15,000 cS.
Suitable non-volatile polyalkylaryl siloxanes include, for example, poly(methylphenyl) siloxanes having viscosities of about 15 to 65 cS at 25xc2x0 C. These siloxanes are available, for example, from the General Electric as SF 1075 methylphenyl fluid or from Dow Corning as 556 Cosmetic Grade Fluid. Additionally, poly(dimethylsiloxane)-(diphenylsiloxane) copolymers having a viscosity in the range of about 10 to 100,000 cS at 25xc2x0 C. are useful.
These and other suitable silicones are disclosed in U.S. Pat. Nos. 2,826,551, 3,964,500 and 4,364,837.
The polymerization process is carried out in the monitored presence of a free radical initiator. Suitable free radical initiators are peroxy esters, peroxide, percarbonates and azo compounds including diacetyl peroxide, dibenzoyl peroxide, dilauroyl peroxide, t-butyl peroxypivalate, t-butyl peroctoate, t-amyl peroxypivalate, t-butyl peroxy-2-ethylhexanoate, di-(4-t-butylcyclohexyl)peroxydicarbonate, 2,2xe2x80x2-azo-bis(isobutyronitrile), 2,2xe2x80x2-azo-bis(2,4-dimethylvaleronitrile), or 1,1xe2x80x2-azo-bis(cyanocyclohexane), and mixtures thereof.
Having generally described the invention, reference is had to the following examples which illustrate preferred embodiments but which are not to be construed as limiting to the scope of the invention as set forth in the accompanying claims.